A lot of computer security is based on trust. Your devices verify that you are, indeed, an authorized user, through the use of user names and passwords. And your devices trust services and servers, through a series of certificates and “trusted third parties” who work through a cascading system of verification and authentication.
If you use Apple devices, the company has its own chain of trust that allows you to use multiple devices in concert. Each link of this chain is carefully designed to ensure its reliability, and each link also enhances other links in the chain. This can seem complex, but when you break it down into its component parts, it’s a lot easier to understand.
In most cases, you don’t need to know how all these elements work together, but it can be good to be aware of how Apple ensures the security of your devices, your accounts, and even your payment methods.
Apple isn’t perfect and I don’t trust the company implicitly but I do trust Apple significantly more than any other company I deal with.